Ultrasound devices may be used to perform diagnostic imaging and/or treatment, using sound waves with frequencies that are higher with respect to those audible to humans. Ultrasound imaging may be used to see internal soft tissue body structures, for example to find a source of disease or to exclude any pathology. When pulses of ultrasound are transmitted into tissue (e.g., by using a probe), sound waves are reflected off the tissue with different tissues reflecting varying degrees of sound. These reflected sound waves may then be recorded and displayed as an ultrasound image to the operator. The strength (amplitude) of the sound signal and the time it takes for the wave to travel through the body provide information used to produce the ultrasound image. Many different types of images can be formed using ultrasound devices, including real-time images. For example, images can be generated that show two-dimensional cross-sections of tissue, blood flow, motion of tissue over time, the location of blood, the presence of specific molecules, the stiffness of tissue, or the anatomy of a three-dimensional region.
With respect to treatment, as an alternative to more invasive types of surgical procedures, many physicians are employing the use of high intensity focused ultrasound (HIFU) as a technique to therapeutically treat internal body tissues. With HIFU, an ultrasound signal of sufficient power (e.g., pressure and velocity) and time is focused on a target volume of tissue in order to change a state of the tissue by rapid heating and/or mechanical destruction by cavitation. The treated tissue may form one or more lesions that may be left in the body and thereafter absorbed through normal physiological processes.
In order to effectively treat tissue, the energy of the delivered HIFU signal must be sufficient to cause the desired physical effect(s). On the other hand, the delivered energy should not be too large or uncontrolled so as to cause unintended collateral damage to healthy tissues surrounding the target volume. The non-homogenous nature of tissue(s) in the body creates variations in attenuation, propagation velocity, and acoustic impedance that modify the expected acoustic wave propagation and deposition of HIFU energy delivered to a target tissue volume when compared to homogeneous material. Thus, certain treatment regimens that are solely based on applying a predetermined dose of HIFU energy may therefore achieve inconsistent results due to such variations.